Modern diesel engines today standardly have so-called common rail systems that make it possible to inject the fuel into the combustion chambers of the internal combustion engine with very high precision under very high pressures. These common rail systems have rail pressure sensors that acquire the pressure in the rail. The pressure is supplied to a control device of the internal combustion engine as an input quantity. Such vehicles have on-board diagnostic systems that continuously acquire and record disturbances of the motor vehicle and of the internal combustion engine. In the field of these on-board diagnostic systems, in particular the OBD2 (On-Board Diagnostics II) systems, there is the legal requirement of monitoring the plausibility for example of data acquired by sensors. In a common rail system, the rail pressure sensor is generally used for two main functions. On the one hand, it is used to regulate the current rail pressure, and on the other hand it is used to determine the quantity of fuel that is to be injected into the combustion chamber. Due to the direct influencing of quantity, the rail pressure sensor is relevant to on-board diagnostics and must therefore be correspondingly monitored.
Various methods are available for the monitoring of the rail pressure sensor. German Patent Application No. DE 10 2006 043 828 A1 describes a method and a device for controlling an internal combustion engine, in particular an internal combustion engine having a common rail system, in which an actual value indicating the fuel pressure is acquired and is compared to a target value. On the basis of the comparison, a control quantity is specified for at least one actuator. A rail pressure quantity is determined on the basis of a quantity that characterizes an electrical quantity of the actuator.
German Patent Application No. DE 10 2008 043 413 A1 describes a method for plausibilizing an output signal of a rail pressure sensor of a direct-injecting internal combustion engine having a common rail system, in which an analog signal, characterizing the rail pressure, of the rail pressure sensor is supplied to a control device and processed in the control device. In this method, the rail pressure sensor outputs an additional digital signal that characterizes the rail pressure, and this additional signal is compared to the analog signal in the control device in order to plausibilize the analog signal that characterizes the rail pressure.
In addition, there exist so-called rail pressure sensor offset tests, which however have the disadvantage that a plausibilization is possible only at the zero point of the rail pressure sensor characteristic curve, and only at times before engine start or during after-running, when the rail pressure has been completely dismantled.
The rail pressure sensor can also work with the aid of a second rail pressure sensor whose acquired pressure data are compared to those of the first rail pressure sensor. However, such a solution requires a high technical outlay and is expensive.